Liquid crystal display has become a prevailing mode of flat panel display. With the liquid crystal display technology widely used in TV set, cell phone and public information display, requirements on display quality of the liquid crystal display panel are gradually increased.
One factor that causes display quality of a liquid crystal display degraded is impurity ions existing in the liquid crystal. Black matrix in the liquid crystal display panel is a main source of the impurity ions. The impurity ions in the black matrix will be aggregated in a region between the black matrix and metal lines under effect of voltages applied on the metal lines in the liquid crystal display panel and permeated to the liquid crystal layer from the region. The impurity ions are main factors for the aging and further the degradation of the liquid crystal material during the operation. The impurity ions will produce adverse effect on the image display under effect of the applied electric field, such as image blur, and degrade display quality of the liquid crystal display panel, thereby deteriorating reliability of the liquid crystal display panel.